The present interest in beryl and chrysoberyl single crystals stems largely from the utility of these crystals as laser host materials. However, the study of methods of making such crystals synthetically dates back to the 19th century, the interest at that time being in making available gemstones at a lower price.
It appeared that two different processes might be employed for the manufacture of such crystals, one being the so-called hydrothermal process and the other being the flux process. Although it has been claimed that Nacken used the hydrothermal process successfully, there is considerable confusion about his work, and recent studies lead to the conclusion that the hydrothermal process was never used successfully.
Emeralds of high quality are now being manufactured by the flux process, but the process is relatively slow, due to the fact that the speed of crystallization is low. In general, the maximum achievable rate using the flux process is about 0.1 mm per day.
A wide variety of fluxes have been used in the attempt to increase the rate of crystallization, examples of such fluxes being Li.sub.2 Mo.sub.2 O.sub.7, Li.sub.2 W.sub.2 O.sub.7, PbMoO.sub.4, V.sub.2 O.sub.5, MoO.sub.3 and B.sub.2 O.sub.3. Where these materials have been used as fluxes, the furnace has generally been heated to about 1000.degree. C. and then cooled gradually. Alternatively, the furnace has been constructed so that a gradient is established. Where attempts have been made to increase the rate of crystallization above that noted above, crystallites are formed.
Using the hydrothermal process, the rate of growth is even lower. Also, the efficiency of production of crystals is low. Nevertheless, since beryl single crystal is an incongruent melting material, high efficiency methods of growing crystals, such as the Czochralski method, have not been utilized.
Chrysoberyl is a beryllium aluminate and is famous as a naturally-occurring jewel stone in the form of cat's-eye, alexandrite, etc. In the attempt to make this stone synthetically, fluxes such as PbO,PbO-PbF.sub.2, PbO-PbF.sub.2 -B.sub.2 O.sub.3 and Li.sub.2 MoO.sub.4 -MoO.sub.3 as well as similar materials have been used as fluxes. However, it has been difficult to obtain large crystals by the use of such flux systems. Moreover, twinning frequently occurs so that it is difficult to obtain single crystals.
In view of the potential utility of chrysoberyl and beryl as laser host materials, it would be eminently desirable that an improved method of producing these materials synthetically in the form of single crystals ranging up to large sizes be available.